A Pew Research Center study indicates the latest violence is part of a rising trend in recent years.

Amateur video captures bomb blast (AP Photo/Rossia TV channel)

A woman from the restive Dagestan province was behind Monday's bus bombing in the in the southern Russian city of Volgograd which killed herself and at least six other people and injured more than 30. The Moscow Times reports that this is the deadliest attack outside of the North Caucasus region since the bombing of Domodedovo Airport in January 2011, when 37 people were killed.

Alexei Malashenko, a North Caucasus researcher at the Moscow Carnegie Center think tank, warned that it could be the first in a series of attacks ahead of the 2014 Winter Olympics in Sochi. “I am very worried, but I believe this is the first bell before the Olympics. We should expect more attacks,” said Malashenko according to the Moscow Times.

The Los Angeles Times reports that It was the latest instance of violence from the Caucasus, fueled by nationalism and Islamic extremism, spilling over into other parts of Russia.

This latest event follows ethnic violence in Moscow earlier this month. The Wall Street Journal reports that police temporarily detained more than a thousand migrant workers to calm tensions following a riot triggered by the killing of a Russian man that residents blamed on a migrant from the predominantly Muslim Caucasus region.

The number of Muslims in Moscow may be as high as three million, according to ITAR-TASS, making Moscow's Muslim population the largest of any city in Europe. The growing numbers are served by only four mosques. The mayor of Moscow has prohibited further mosque constructions, arguing that most of the Muslims are temporary residents, also according to ITAR-TASS.

A recent Pew Research study finds that social hostilities involving religion in Russia such as these have been rising in recent years, predominantly driven by tensions emanating from the Caucasus. Religious hostilities have been rising in Europe as a whole, including increasing by more than twofold in Russia between mid-2006 and the end of 2011, as shown in the chart below.

In Russia last week, the threat of U.S. missiles targeting Syria in retaliation for the regime's alleged use of chemical weapons weighed heavily on world leaders meeting for the G-20 summit n St. Petersburg, eclipsing economic battles that usually dominate the summit.

Russia's President Vladimir Putin has been a vocal critic of U.S. plans to intervene in the affairs of Syria, an ally of Russia, and home to a Russian naval base - Russia's last remaining military facility outside the former Soviet Union.

Though religious connections between Russia and Syria are not central to the dispute, several commentators have noted the connection between faith communities in the two countries. Though Syria is predominantly Muslim, it has a substantial number of people belonging to the Christian Orthodox Church, the majority faith of Russia, and a church with considerable influence in the government. Walter Russell Mead notes in a recent blog post:

Russia’s concern for Syrian Christians is also nothing new. Although the Communists were more interested in hounding and enslaving religious believers than protecting them, under the czars Russia was officially recognized by the Ottoman sultans as the protector of Orthodox Christians throughout the Turkish empire. In the 18th and 19th century Russian concern for these Christians (married to a concern for its geopolitical ambitions) frequently shaped Russian policy towards the Ottomans and the West. The Crimean War at one point brought Russia into war with Britain, France and the Ottoman Empire over a quarrel between Russia and France over their rights to represent and protect Ottoman Christians in the Holy Land.

Here are 2 things to know about religion in Russia from recent Pew Research studies.

1. Straddling Europe and Asia, Russia could be considered the most populous Christian-majority country on both continents.

But for the purposes of a recent Pew Research report, Russia is considered a European nation. Its 105 million Christians constitute the world’s fourth-largest Christian population (and the single largest outside the Americas). About 5% of the world’s Christians live in Russia. Moreover, Russia is home to the largest autocephalous (or ecclesiastically independent) Eastern Orthodox Church in the world, the Russian Orthodox Church.

Byzantine monks first introduced Christianity into Russia in the 9th century. Following his baptism in 988, Vladimir I, the prince of Kiev, led his people into Christianity. The Eastern Orthodox Church has remained the largest religious institution in Russia despite monumental changes in the country’s political system, from monarchy, to Soviet communism, to the current parliamentary and presidential system. Today, a little more than 70% of Russia’s population identifies as Orthodox.

While Orthodox Christianity is still the dominant religion in Russia, other Christian traditions have grown in recent decades. Outside of the Orthodox Church, Protestants constitute the largest Christian group, with nearly 3 million adherents. A large segment of the Russian population does not identify as Christian, including many who are unaffiliated with any particular religion. According to a 2011 Pew Forum report, Russia has the largest Muslim population in Europe (in absolute numbers).

2. Russia has the largest Muslim population in absolute numbers in all of Europe.

According to a report by the Pew Research Center, the number of Muslims in Russia is projected to increase from about 16.4 million in 2010 to about 18.6 million in 2030. The Muslim share of the country’s population is expected to increase from 11.7% in 2010 to 14.4% in 2030.

The growth rate for the Muslim population in the Russian Federation is projected to be 0.6% annually over the next two decades. By contrast, Russia’s non-Muslim population is expected to shrink by an average of 0.6% annually over the same 20-year period.

Several factors contribute to the projected growth of Russia’s Muslim population. For instance, Muslim women generally have more children than other women in Russia (an estimated 2.3 children per woman, compared with a national average of fewer than 1.5 children per woman). Higher Muslim fertility is directly related to the fact that Muslim women marry in larger numbers and divorce less often than other women in Russia. This means they spend longer periods of their lives in unions where childbearing is more likely. And although the abortion rate in Russia is still among the highest in the world, research suggests that Muslim women have fewer abortions on average than other women in Russia.

Another reason the Muslim population in Russia is expected to increase is that nearly half of the country’s Muslims are under age 30, according to an analysis of data from Russia’s 2002 census. By comparison, about 40% of ethnic Russians are in this age group. Nearly a quarter of Russia’s Muslims (22.8%) are under age 15, compared with roughly one-in-six ethnic Russians (15.9%).

On the older end of the age spectrum, about 27% of Russia’s Muslims are age 45 and older, compared with about 38% of ethnic Russians. And 13.1% of Muslims in Russia are age 60 and older, compared with nearly a fifth of the ethnic Russian population (19.1%).

The Muslim population in Russia is geographically concentrated in a few regions. As of 2009, four-in-five Muslims in Russia resided in two of the seven federal districts, the Volga and Southern districts. Among the 89 sub-regions of Russia in 2009, Muslims were concentrated in five traditionally Muslim homelands: Dagestan (16.3% of all Muslims), Bashkortostan (14.6%), Tatarstan (13.5%), Chechnya (7.4%) and Kabardino- Balkaria (4.7%). Smaller numbers of Muslims lived in three other Muslim homelands: Ingushetia (3.0% of all Muslims), Karachaevo-Cherkessia (1.9%) and Adygea (0.8%). Altogether, about two-thirds of all Muslims in Russia (62.3%) resided in one of the traditionally Muslim homelands.

Moscow has become a migration magnet for people from elsewhere in Russia, as well as beyond Russia. More than 600,000 Muslims reside in Moscow (3.7% of all Muslims in Russia) and an additional 517,000 live in the oil-rich Tyumen region (3.0%), which borders Kazakhstan to the south.

For a discussion of global social hostilities involving religion and government restrictions on religion, with Russia's place in relation to other countries, see my TEDx Talk.